The invention relates to a substrate provided with a polycrystalline diamond layer.
Diamond is an interesting material which, owing to its excellent characteristics, can be used for many different purposes. Firstly, owing to its extreme hardness, it is used in abrasion tools; secondly, its particularly good thermal conductivity in conjunction with a high electrical resistance is utilized for dissipating heat from electronic components.
Diamond for the last-mentioned application is usually prepared by a polycrystalline diamond layer being deposited on a substrate, e.g. with the aid of PVD or CVD processes (Physical or Chemical Vapour Deposition).
In these deposition processes the diamond layer builds up by a very large number of small crystals being initially formed directly on the substrate surface and then growing together to produce a small number of large crystals in the subsequent growth process.
As it happens, measures are known for enabling the formation of as many crystals as possible, i.e. increasing the grain density on the substrate. As a result, the individual crystals will grow together more rapidly, so that the actual layer growth can start sooner and the entire growth process can thus be accelerated.
While these measures allow the thermal conductivity of the diamond layer as a whole to be improved, it is still not particularly satisfactory, for example in view of the high packing density of electronic components, in particular power components.